It is known that today's storage media like optical storage media or hard disks change their behavior over the years, e.g. due to aging, temperature differences, or in the case of rewritable storage media, due to multiple read/write cycles. Apart from these effects, the reading performance is also reduced through damage of the storage media, e.g. scratches and/or fingerprints in the case of optical storage media. In the worst case these effects result in the loss of the whole data on such a storage medium. Therefore, it is of high importance to detect a decrease of the quality of a storage medium early enough to transfer the recorded data to a new storage medium.
For this purpose, when archiving important information on recordable DVDs, professionals use dedicated testers to measure the amount of error correction needed to read a recorded DVD. The measured quality parameters are entered into a database, which is archived as well. After a few years some of the DVDs are sampled, i.e. the quality is measured again and compared with the previously measured parameters. This allows to determine how quickly the DVDs are deteriorating. The advantage of using a DVD as a long-term storage medium is its widespread format, ensuring that readers will still exist decades from now. The drawback is its unpredictable durability. A drawback of the independent database for recording the quality parameters is that it is proprietary. Therefore, it is questionable whether it will be usable after many years.
In a different environment, high-speed DVD recorders are emerging on the market for professional and semi-professional applications, e.g. for storing multimedia content such as audio and video data, or software, on demand on a DVD. The quality of the recording is paramount in such applications, as it translates directly into a better playability, i.e. the percentage of legacy players capable to read the recorded DVD, and better longevity, i.e. the number of years that the DVD is readable without exceeding the capability of its built-in error correction mechanism. Therefore, also for such applications it is advantageous to detect a deterioration of the storage medium.
Even in consumer applications it may be desirable to check if important recordings are deteriorating. Software tools are available for analyzing a storage medium with respect to the error rate. For example, after recording an optical disk such a tool can be used for checking if there are enough margins for playability. In addition, commercial recording software often offers verify functions, which can be used for this purpose. In addition, some consumer electronics devices already have the capability to inform a user about the error rate. For example, EP 0 073 519 discloses an optical disk player, which during playback automatically determines the error rate of the disk and indicates the error rate to the user. However, as for less professional users an independent database for recording the determined quality parameters is not a realistic way to verify the condition of a storage medium, the user has no convenient possibility to monitor the degradation of a storage medium.